Since the phone call while driving may distract the driver, in order to prevent this, the hands-free phone call has been widely used for enabling the driver to concentrate on driving without the use of hands.
Early hands-free device is wired and mounted on a mobile phone holder, but in recent years, the product, in which Bluetooth technology is applied so that the phone call is possible even while leaving the mobile phone in a bag or pocket, has gained popularity.
Bluetooth is the technology according to the specification of the IEEE 802.15.1 short-range wireless communication technology, and it allows the electronic devices, such as a wireless terminal located within about 10 m, for example, a computer, a cell phone, a headset, a PDA, a printer, a mouse, a keyboard and the like, to wirelessly communicate with each other in a low cost and low power.
General Bluetooth hands-free devices output the audio signal transmitted from the paired mobile phone or MP3 player through the speaker provided in a vehicle, and transmit the user's voice signal inputted through the microphone provided in a vehicle to the mobile phone when call function of the mobile phone is used.
Conventional Bluetooth specification was defined so that a Bluetooth device connects when the request for the connection is received and disconnects when the request for releasing the connection. On the basis of this specification, in most cases, the Bluetooth connectivity is maintained in the disconnected state when it is disconnected due to an error of one of devices and there is a problem that it is not reconnected. Also, in the process of applying the Bluetooth technology to a vehicle, the problem that a Bluetooth device is disconnected but not reconnected frequently occurred and this problem causes customer dissatisfaction.